I found some interesting pictures of CFM56-3 and CFM56-7B engines on the database. What I found most interesting was the differing generator setups, and the changes this makes to the fan cowlings. It appears the -3 has a separate CSD / generator set-up, whilst the -7B has an IDG. Was it possible to get an IDG fitted to the -3?

The fan cowlings of the -3 seem to be much longer to allow for access to the generator. Is the remaining part of the inlet cowl readily separated from the rest of the engine? The -7B has an inlet cowling of the type that is more familiar to me.

The side mounted gearbox is an interesting set-up. From the looks of it, there appears to be what I assume is a shrouded shaft at the top rear of the gearbox, which itself ends up at another box like structure. Does this box contain a set of bevel gears? Does the driveshaft from the engine core come out "sideways" through one of the fan case struts?

Not to my knowledge. Boeing reverted to the older IDG design for the NexGens due to reliability issues and cost issues (cough cough, Southwest strikes again).

The remainder of the inlet cowl looks like it comes off in the customary way, on both airplanes... lots of twelve point bolts!!!
But then, I'm familiar with PRATT powered 737s, so I might be predisposed to think that.

Fair enough. The -3 design is interesting however, as the only time I have seen a nose cowl look like that is when the outer skin was de-riveted and removed in the sheet metal shop. The inner skin must be a fair bit thicker to maintain the required amount of stiffness

Quoting Mender (Reply 4):However some 737 classics have Variable Speed Constant Frequency generators but these are not that common

All the BA B737-400s were delivered with VSCF.

But after many years of problems with them it was finally decided that it was worth removing them, and now they are no more. They really were unreliable, perhaps a bit ahead of their time. The problem was the electronics that converted the output to constant frequency were mounted on the VSCF, where I suppose they should have been fitted in the airframe.

Quoting JetMech (Thread starter):
The side mounted gearbox is an interesting set-up. From the looks of it, there appears to be what I assume is a shrouded shaft at the top rear of the gearbox, which itself ends up at another box like structure. Does this box contain a set of bevel gears? Does the driveshaft from the engine core come out "sideways" through one of the fan case struts?

JetMech,

This "box" you refer to is the Transfer Gearbox (TGB), it connects to the Internal gearbox (IGB) located at the front of the N2 (HP) compressor spool. The main Accessory gearbox (AGB) is mounted on the left side of the fan frame. It was mounted here by CFMI to give extra ground clearance for the 737.

A transfer drive shaft connects the IGB and TGB which runs inside the 9 o' clock fan frame strut when viewed from the rear. There is another drive shaft (which you identified as shrouded) between the TGB and the AGB. Only the IGB & TGB have beveled gears. The the drive shaft from the TGB to the AGB is located in splines and held in place with a large nut during installation.

Only the -3 and -7 CFMs have the AGBs mounted at the 7/8 o'clock position. -5A, 5B & 5C engines have the TGB and AGB mounted at the 6 o'clock position as there is plenty of ground clearance on Airbus aircraft.

Nice picture! It's good to see that there is still a place for good old fashioned mechanical components in something as sophisticated as a jet engine.

Quoting CFMTurboFan (Reply 7):Only the -3 and -7 CFMs have the AGBs mounted at the 7/8 o'clock position. -5A, 5B & 5C engines have the TGB and AGB mounted at the 6 o'clock position as there is plenty of ground clearance on Airbus aircraft.

I see. I suppose this was more in line with the original engine design? IIRC, the 737 runs the side gearbox arrangement, which actually is the modified version.